1. Field of the Invention
The present invention relates to an electroplating process for an Oldham ring preventing the autorotation of an orbiting scroll member and having a uniform plating thickness, and a scroll member type compressor comprising the same.
This application is based on Japanese Patent Application No. Hei 10-204075, the contents of which are incorporated herein by reference.
2. Description of the Related Art
A compressor is provided as a refrigerator in air conditioning systems such as an air conditioner provided in a car. The compressor compresses a gas refrigerant supplied from an evaporator, and expels the gas refrigerant under high temperature and high pressure.
Various types of compressors containing a scroll member type compressor have been suggested. The scroll member type compressor comprises a fixed scroll member and an orbiting scroll member which respectively have a spiral wrap. The orbiting scroll member eccentrically orbits relative to the fixed scroll member while the spiral wrap comprising the orbiting scroll member engages the spiral wrap comprising the fixed scroll member. Specifically, the position of the fixed scroll member is displaced 180.degree. behind in an orbiting direction of the orbiting scroll member. An Oldham ring is provided on the rear surface of the orbiting scroll member. The Oldham ring allows the orbit of the orbiting scroll member relative to the fixed scroll member, but prevents the autorotation of the orbiting scroll member. A space is made between the spiral wraps, because the position of the fixed scroll member is displaced 180.degree. behind in an orbiting direction of the orbiting scroll member. That is, a compressed space is made between the spiral wrap of the fixed scroll member and the spiral wrap of the orbiting scroll member. Refrigerant is introduced in the compressed space, then the orbiting scroll member eccentrically orbits relative to the fixed scroll member. Therefore, the compressed space is compressed so that the central part of the compressed space is more compressed than the circumferential part thereof Thereby, the refrigerant is compressed depending on the orbit of the orbiting scroll member relative to the fixed scroll member.
When a mixture containing a refrigerant and an oil is introduced in the compressor, the oil contained in the mixture is stirred by the orbiting scroll member, Oldham ring, and the like; whereby the scroll member type compressor is lubricated. However, when the compressor is not used for a long time, the oil coating the Oldham ring accumulates at the bottom of the compressor. Therefore, oil cannot instantly coat the Oldham ring when the compressor starts up after long disuse time. At this time, it is possible that the compressor is scorched because the absence of a lubricant.
In order to prevent such scorching, electroplating an Oldham ring made of iron sintered metals with tin has been suggested. The anti-scorching property of the Oldham ring is remarkably improved by the electroplating. FIG. 5 shows this electroplating process. In FIG. 5, the Oldham ring 1 is immersed in the plating liquid L containing sulfuric acid and tin sulfate. Ends 2 and 2 of a cathode, that is, electrodes are placed at the upside and the downside of the inside wall of the Oldham ring 1. That is, the electrodes 2 and 2 are placed near the key portions 3a and 3c of the Oldham ring 1. In addition, the electrodes 2 and 2 can be placed at the right side and the left side of the Oldham ring 1. That is, the electrodes 2 and 2 can be placed near the key portions 3b and 3d of the Oldham ring 1. For example, when the electrodes 2 and 2 are located near the key portions 3a and 3c, almost all of current flows to the key portions 3a and 3c. Therefore, the key portions 3a and 3c are electroplated more thickly than the key portions 3b and 3d. In contrast, when the electrodes 2 and 2 are located near the key portions 3b and 3d, almost all of the current flows to the key portions 3b and 3d. Therefore, the key portions 3b and 3d are electroplated more thickly than the key portions 3a and 3c. When the electroplated layer of the key portions is thicker than the electroplated layer of other key portions, it is difficult to fit the key portions in grooves formed in the element other than the Oldham ring. That is, it is difficult to smoothly fit the Oldham ring to other elements.